It is known to improve seed germination, with this type of prior art being illustrarted by U.S. Pat. No. 2,553,577 to Hale et al., and U.S. Pat. No. 2,690,388 to Hale. Treatment of a seed with a microorganism, particularly with a microorganism of the genus Phizobium, is also known. This type of prior art is exemplified by U.S. Pat. Nos. 2,313,057 to Fischer, 3,168,796 to Scott et al, 3,499,748 to Fraser, 4,136,486 to Franklin, Jr. et al, 4,149,869 to Lloyd, and 4,161,397 to Bellet et al. In addition, U.S. Pat. No. 674,765 to Hartleb who discloses a seed treated with a microorganism, states that nodule formation begins very shortly after the seed has become imbedded in the soil, and mentions rapid germination at lines 37 and 38 thereof. Furthermore, U.S. Pat. No. 4,077,793 to Krupicka discloses that treating seeds of certain crops such as maize, corn, potatoes ad tomatoes with a biochemical material containing nitrogen-fixing soil microorganisms results in earlier germination, and reports unusually good yield. Also, Chemical and Engineering News, Dec. 8, 1980, p. 29 discusses the treatment of soybean seeds with nirogen-fixing bacteria.
Additionally, it is known to stimulate the sprouting of cucumber and sugar beet plants by spreading a cell suspension of Agrobacterium rhizogenes on the surface of cucumber and sugar beet seeds. Illustrative of this type of prior art is M. Stanek, Foila Microbiologica 21(3):213 (1976). In this work, the microorganism was isolated from the surface of the hyphae of the fungus Pythium debaryanum. It is also disclosed in this work that treatment of the surface of sugar beet seeds with a suspension of the A. rhizogenes cells prevented black root disease, when the seeds were simultaneously artificially contaminated with the fungus Phoma betae.
Finally, the preparation of an infectivity-cured Hr plasmid-bearing microorganism is known. Illustrative of this prior art is Moore, Warren and Strobel, Plasmid, 2:617-626 (1979). This microorganism was prepared by treating A. rhizogenes A.sub.4, which contains the Hr plasmid in nature, with ethidium bromide. This microorganism was free from pathogenicity to carrots. In this work, it is suggested in the paragraph bridging the two columns on p. 625 that induction of rooting may be a potential use of A. rhizogenes A.sub.4. Induction of rooting is a potential use of pathogenic A. rhizogenes A.sub.4 and is to be distinguished from either induction of germination (sprouting) or growth promoting activities such as the enhancement of root elongation, shoot elongation, and root development.
However, this and the other prior art of which we are aware, are deficient as failing to provide an agriculturally useful composition comprised of a seed treated with a selected infectivity-cured Hr plasmid-bearing microorganism. Furthermore, this art fails to provide methods of enhancing root elongation, shoot elongation or root development of a germinating seed that include treating a seed with a selected infectivity-cured Hr plasmid-bearing microorganism. Moreover, this prior art fails to provide a method of inducing germination of Kentucky bluegrass seed that involves treating the seed with a selected infectivity-cured Hr plasmid-bearing microorganism, and fails to provide a method of promoting plant growth at a lower soil temperature than is common at the time of planting a seed of the plant. Additionally, this prior art fails to provide an inoculant for increasing nodulation, root mass, and shoot mass in a leguminous plant, the inoculant containing a Rhizobium microorganism and a selected infectivity-cured Hr plasmid-bearing microorganism; and fails to provide an agriculturally useful composition containing a suitable seed treated with this inoculant.